The invention concerns a test process for drawn arc working stud welding guns and also a circuit arrangement for carrying it out.
In drawn arc stud welding, the stud welding gun, with the welding stud held by it, is placed on the workpiece. A switch is thereafter operated so as to produce a small current over the welding stud to the workpiece. Because of the operation of the switch, the welding stud is raised by means of a lifting solenoid contained in the stud welding gun, whereby a relatively weak arc is produced between the welding stud and the workpiece. In this operating condition a welding current supplied from a condensor battery is added which causes the welding stud and the opposing surface of the workpiece to melt. Finally, with the welding current still flowing, the welding stud is brought up to the workpiece again and dips into the melted part of the workpiece and this completes the welding operation.
The use of a rectifier for supplying the welding current is in principle also possible for the process described above. In practice however the condensor battery is generally used as a source of energy for the welding current for specific applications. The current impulse supplied by the condensor battery is very short and lasts about 6-10 milliseconds. The feed movement of the welding stud must be matched to this short period of time, that is the movement of the welding stud and thus the mechanical design of the stud welding gun are of decisive importance for the quality of the weld. In order to create conditions as clearly defined as possible for the feed movement a definite value has been placed up to now on the mechanical design of the stud welding gun and particularly on the progress of its movements, whereby correspondingly high requirements are placed on the components of the stud welding guns concerned with the progress of the movements.
It has however been shown that nevertheless the movements in stud welding guns of all types, and particularly the feed movement, are subject to considerable fluctuations. The welding results were better or worse because of these fluctuations. This problem has been attacked up to now by first carrying out test welds of which the welding results are then examined in order thus to determine whether a stud welding gun gives optimum results. When it was found that the welds were unsatisfactory, the cut-out of the lifting solenoid of the stud welding gun produced by the starting signal was shifted with regard to the time it occurred. To do this several cut-out moments had to be tried out and without, except in rough cases, it being ascertainable in advance whether the times (moments) had to be advanced or retarded. In this way an optimum setting was finally found after a few try-outs. In subsequent operation of this optimum setting however, there were variations caused by the changing of the mechanical working time of the gun so that afterwards the optimum value had to be checked time and again by means of tests. This resulted not only in loss of time and materials before the stud welding gun could be used, but in interruptions in production which were untenable, particularly in the case of conveyor belt production where stud welding guns are frequently used.